The present invention generally relates monitoring the freezing temperature of fuel onboard a vehicle. More specifically, the present invention relates to monitoring the freezing point of jet fuel onboard an aircraft.
In recent years, Russia officially opened Russian airspace to commercial airlines and flight routes over the North Pole are available for use. An era of commercial transpolar flight has begun, offering an unprecedented efficient and economic link between cities of North America, Asia and Europe. The polar routes are extremely attractive to the airlines and their customers for many reasons, the paramount of which being faster non-stop services between such major centers as New York and Hong Kong, cutting up to six hours off regular travel time. For the first time, airlines can offer faster, possibly cheaper, flights between the world""s most important business centers. Not only is non-stop service highly attractive for the travel-weary customer, there are also numerous benefits for the airlines. In addition to significant fuel savings and reduced amount of operation time and labor cost, there is the further benefit of a smoother flight due to a lack of headwinds along these routes during the winter months.
With any significant change in flight operations, a thorough review of the technical challenges involved and their possible impact on aircraft safety is critical. With polar flights, there are two particular issues related to the freezing point of the jet fuel on the aircraft. Should the jet fuel in the wing tanks reach its freezing point, there is a possibility of the following: (1) The flow of fuel to the engine becomes blocked, causing the engine to stutter and, possibly, loss of the aircraft; or (2) the fuel solidifies and becomes trapped within tanks, curtailing the amount of useful fuel available to the engine. Certainly, the scenario of fuel freezing has always been an important consideration, even for regular flights. However, with polar flight, this issue is heightened as the aircraft is often flying in outside ambient temperatures that can commonly reach minus seventy degrees Celsius (xe2x88x9270xc2x0 C.) or colder. Flying over the North Pole""s large permafrost and the drastic reduction in sunlight during the winter months means an increase in the possibility of fuel in the wing tanks reaching its freezing point. All outbound aircraft in the US are dispatched with Jet A fuel, with a specification freezing point of xe2x88x9240xc2x0 C. With no means of testing the fuel as it is being uploaded to each aircraft, the pilot must fly assuming that the freezing point of the fuel in the aircraft is xe2x88x9240xc2x0 C. as specified.
Various published studies have confirmed that the fuel temperature in the wing tanks of about fifty percent (50%) of certain scheduled polar flights fall to within 3xc2x0 C. above freezing point specification. This amount of cooling in the fuel is significant for most aircrafts, as pilots are directed to perform mandatory corrective measures to warm the fuel, if and whenever the fuel temperature falls to xe2x88x9237xc2x0 C. These measures include increasing aircraft speed, descending to a lower altitude and/or maneuvering around the cold-air cell. Aside from the fact that pilots prefer to avoid any change in flight operations, these corrective measures result in significant expenses for the airlines. Therefore, the benefits of flying polar, such as less time less fuel and smoother flight, will not be fully realized. However, a survey of seven major gateway airports in the US has demonstrated that the fuel being uploaded into each aircraft often has a lower freezing point then the required xe2x88x9240xc2x0 C. If this freezing point temperature can be certified, many of the corrective actions described above could be rendered unnecessary.
In the absence of an onboard system, the safety of an aircraft flying a long-range polar route must depend on the knowledge of the fuel temperature during flight, coupled with the assumption of the fuel freezing point. If the assumption is conservative, which is often the case, the aircraft is inefficiently operated because of the many unnecessary xe2x80x9ccorrective actionsxe2x80x9d. If the unexpected scenario occurs of the actual freezing point of the fuel being warmer than the specification value, the outcome could be catastrophic. It should be noted that ground-based freezing point analyzers have been available for quite some time. However, these ground-based analyzers lack the ability to collect a representative sample inside the aircraft fuel tank. These ground-based analyzers can at best monitor the freezing point of the fuel being loaded into the fuel tank, but frequently the pilot is more interested in the freezing point of the composite fuel that is onboard the aircraft and being delivered to the engines during flight. The composite fuel is made up of the fuel from the current fill as well as residual fuels in the aircraft tanks that originated from previous airports. Since the amount and chemical composition of residual fuel vary, and the mixing of fuels is not uniform inside the multiple fuel tanks that are separated by baffles, it is impossible to predict or correlate the freezing point of the composite fuel based on information generated by ground-based freezing point analyzer. In fact, the freezing point of the composite fuel could be different from that measured by the ground-based analyzer by up to several degrees Celsius. This amount of difference is often sufficiently important to decide whether corrective action should or should not be taken.
In order to incorporate a fuel analyzer into an aircraft, there are important restrictions to be satisfied. These restrictions are often not considered or applicable for ground-based systems. For instance, space is in short supply in the aircraft in general and particularly in the fuel tank area, the size and weight of the device becomes a key issue. Equally important is the manner in which the device is implemented due to its proximity to a large amount of highly flammable material. There are other requirements for aircraft-mounted device that ground-based instruments cannot readily satisfy. For example, aircraft-mounted device must have a minimum demand on utilities as they are not conveniently available. Some ground-based systems require the consumption of liquid carbon dioxide for cooling or the consumption of dry and compressed nitrogen for purging and cooling. However, liquid carbon dioxide and compressed nitrogen are disallowed in aircraft because of high pressure storage requirement and because both are asphyxiants. Moreover, an aircraft-mounted device must be rugged enough to withstand vibrational shocks that could take place during unusual situations such as extreme turbulence or loss of function of an engine. Wherein, some ground-based systems require multiple pieces of delicate glassware, some of which are double-walled to hold the fuel sample and coolant. Such delicate apparatus would not be very suitable for a mounting inside an aircraft.
It is an object of the present invention to provide a device useable in an aircraft that is capable of determining the freezing point of fuels so that flights vulnerable to enroute low temperature fuel delivery problems could be conducted safely and efficiently.
A fuel freezing point monitoring device having a test chamber with an internal channel for retaining a fuel sample. There is input into said test chamber to allow input of the fuel sample. There is an output out of said test chamber to allow exiting of the fuel sample. There is a cooler in thermal contact with said test chamber for cooling the fuel sample in said test chamber. There is a light transmission path along said internal channel having an entrance into said test chamber and an exit out of said test chamber. There is a light source which directs light into said entrance of said light transmission path and a light detector to detect light level from said light source exiting said exit of said light transmission path.